Rotating anode x-ray tube



z. J. ATLEE ETAL 2,233,194

ROTATING ANODE X-RAY TUBE Feb. 25, 1941.

Filed 001'.. 26, 1938 Figi,

Inventors: `vZed J. Atlee. Malvern J. Gross,

Them Attovney.

Patented Feb. 25, y1941 ROT'ATING AN ODE X-RAY TUBE Zed J. Atlee, Elmhurst, and Malvern J. Gross, Chicago, Ill., assignors to General Electric X-Ray Corporation, Chicago, Ill., a corporation of New York Application october 2s, 193s, serial No. 237,026

3 Claims.

The present invention relates to improvements in X-ray apparatus of the type which includes an X-ray tube having a stationary cathode and a relatively rotatable anode or target.

In such tubes the various elements of the target face are caused successively to intercept an eiectron beam projected from the cathode. Since the latter is presumably stationary, the focal spot produced by impingement of the beam on the target should appear of constant dimensions and fixed position. It has beennoted, however, that in tubes of the type in question the focal spot sometimes assumes a blurred aspect, indicative of some motion of the electron beam itself.

We have found that this diiiiculty may be overcome, especially in connection with tubes of all-glass construction, by providing magnetic shielding means interposed between the discharge space and the electromagnetic structure used for rotating the anode.

the electron beam by the rotating magnetic iield which such structure produces.

The features which we desireto protect herein are pointed out in the appended claims. The details of the invention, however, may best be understood by reference to the particular construction shown in the drawing in which Fig. 1 is a longitudinal sectional View of an X-ray tube suitably embodying the invention, and Fig. 2 is a diagrammatic representation on a Vreduced scale showing the tube of Fig. 1 enclosed Within an insulation-filled container.

The apparatus illustrated in Fig. 1 comprises an elongated envelope I0 which consists mainly of glass and which is of a generally cylindrical outline.

Toward the right-hand end of the envelope there is provided a cathode comprising a filament It, shown in dotted outline, and a focusing body i3.

The latter is associated with the filament in such a way as to concentrate the electrons emitted therefrom into a focused beam. Lead-in connections I4 and I5 permit heating current to be supplied to the filament l2. There is also shown in connection with the cathode structure a shielding housing I6 which serves to protect the cathode lead-in seal and to reduce the amount of secondary radiation through the end of the tube.

in spaced relation to the cathode there is provided a rotating anode having an inclined target face I8.

The anode is rotated at relatively high speed by means of an induction rotor element which suitably comprises a cylindrical iron core 2Q having a squirrel cage or other winding (not shown) A further extension of the anode struc- (Cl. Z-148) ture comprising a body 2l of good heat conducting material may be provided to increase the heat dispersing capacity of the 'structure as a whole. The part 2l as well as the other parts of the anode may be coated externally with a 5 blackening material which serves to improve heat radiation therefrom.

For supporting the anode and for supplying current thereto, there is provided a shaft 23 which extends into the interior of the discharge 10 envelope through a glass-to-metal seal (not shown). The shaft and the rotating parts are separated by means of anti-friction bearings (not shown) which permit free rotation of the anode structure.

In order to supply a driving force to the rotor 2B, there is provided outside the envelope an electromagnetic stator structure of known type. This comprises a laminated iron core member 25, arranged to surround the envelope, and energizing windings 26 wound in slots of the core member. It is the function of the stator structure to provide a rotating magnetic field which operates to drive the rotor 2i). To this end the windings 26 may be energized either from a polyphase source or from a single phase source through a phase-splitting connection.

In operation, a sufliciently high potential is applied between the cathode and anode to produce a beam of electrons (indicated in dotted outline at 30) which impinges on a selected region of the target face. On such face the beam forms a focal spot which may be circular or elongated as the condition of use may require. The X-rays which are generated at the target face by the action of the impinged electrons are permitted to escape from the envelope through a window 32 which comprises a thin portion of the envelope wall.

In connection with the use of an 'X-ray device such as that described, the focal spot, which should be of small dimensions for best results, sometimes assumes an enlarged or blurred appearance. Apparently this is due to the action of the magnetic field produced by the stator 25 in causing oscillatory motion of the electron beam. It appears that the rotating field created by the stator acts on the beam, moving it back and forth or orbitally in synchronism with the rotation oi the field.

Our invention avoids this difiioulty by providing between the stator structure and the interelectrocle space a special shielding member adapted to prevent the effects of the magnetic field from extending into the space. This member may be provided either inside or outside the envelope enclosure. (If inside, its potential should be fixed as by connection to the cathode.) In the construction illustrated the member takes the form of a substantially continuous external sleeve 34 of steel or other magnetic material which extends from the core 25 to and beyond the region which encloses the discharge path. It is the function of this sleeve to provide a low reluctance path for the magnetic flux produced by the stator and to prevent such iiux from extending into the discharge space. By its use, one avoids the magnetic displacement of the electron beam referred to in the foregoing.

In connection with the sleeveV 34 `thereis provided an additional sleeve 35 which is constituted of an X-ray impervious substance such as lead and which serves to reduce radiation of X-rays in undesired directions. There is also provided a continuous imperforate cylinder 36 of an insulating material such as a phenolic condensation product which extends along the entire length of the discharge envelope and which is interposed between the envelope `and the stator structure. The elements 34 and 35 are preferably provided with aligned openings adjacent to the Window 32 so as to avoid obstruction of the X-rays.

The invention described in the foregoing is considered primarily useful in apparatus Where the X-ray producing device is to be enclosed in an oil-filled casing. In such use the need for compactness requires a construction in which the electromagnetic structure is in close proximity to the inter-electrode space so that its eiiect on the electron beam is exaggerated. This type of construction is exemplifiedby the tube shown in Fig. 1 of the drawing and its incorporation in an enclosing casing is illustrated schematically in Fig. 2. In the latter figure, the casing, which is adapted to be filled with oil, isindicated at 38.

While we have described our invention in connection with a particular embodiment thereof, 'it will be understood that numerous variations may be made by those skilled in the art Without departing from the invention. We, therefore, aim in the appended claims to cover all such equivalent variations as come within the true spirit and scope of the foregoing disclosure.

What We claim as new and desire to secure by Letters Patent of the United States is:

'magnetic material applied externally to the envelope in a region which surrounds the interelectrode space and in which it effectively shields such space from the magnetic eld extending from the stator structure, thereby to prevent de- Iiection of the electron stream by the said eld.

2. An X-ray apparatus comprising an elongated glass envelope, a stationary cathode and a rotatable anode defining a discharge space therebetween, means associated with the cathode for L' focusing theelectrons emitted thereby into a convcentrated stream, a rotor for driving the anode positioned relatively remote from the discharge space, an electromagnetic stator having an iron core which symmetrically surrounds the envelope in a `region adjacent to the rotor, and a sleeve of magnetic material outside the envelope and extendingfromthe iron core of the 4stator to a region which `surrounds the discharge space, the said sleeve serving to shield the discharge space from-the stator field.

3. An 'X-ray apparatus comprising an envelope consisting substantially entirely of glass, a stationary cathode and a rotatable anode Within the envelope, focusing means associated with the cathode for directing a concentrated stream of electrons from said cathode toward a restricted @area of said` anode, a rotor connected to the anode forfdriving the same, an electromagnetic stator `structure symmetrically surrounding the envelope, Said structure being eiective When encrgized to produce a rotating magnetic field of a character adapted simultaneously to cause rotation vof said rotor and to produce objectionable oscillatory deflection of said electron stream, and a 'shield of magnetic material separate from the envelope and? interposed between the stator structureiand the path of the electron stream for preventing the said oscillatory vdeflection of the stream.

.ZED J. ATLEE. `MALVERN J. GROSS. 

